Water-base coating material

ABSTRACT

Disclosed is an aqueous coating agent comprising a water dispersion (C) prepared by dispersing resin particles containing a water-dispersible polyurethane resin (A) and at least one compound selected from a hydrophobic polyester polyol (B-1) and a hydrophobic polyether polyol (B-2) in water, and a crosslinking agent (D) capable of reacting with a hydroxyl group, wherein the water-dispersible polyurethane resin (A) is obtained by reacting a polyester polyol (a-1), which is obtained by condensing a dicarboxylic acid containing an aromatic dicarboxylic acid as a main component with a polyol, with a polyisocyanate, and also contains 15 to 35% by weight of an aromatic cyclic structural unit, and wherein the hydrophobic polyester polyol (B-1) and/or the hydrophobic polyether polyol (B-2) are liquid at normal temperature and contain 20 to 50% by weight of an aromatic cyclic structural unit.

TECHNICAL FIELD

The present invention relates to an aqueous coating agent. Moreparticularly, the present invention relates to an aqueous coating agentthat can be applied as primer coating agents which are used for thepurpose of modifying the surface of plastic films made of polyesterresin, polypropylene resin and polyamide resin thereby to impartexcellent adhesion; anchor coating agents which are used for the purposeof improving adhesion to an aluminum deposit layer of analuminum-deposited plastic film in the production of thealuminum-deposited plastic film; coating compositions, inks; and surfacetreating agents for fibers and leathers.

This application claims priority from Japanese Patent Application No.2003-150608, filed on May 28, 2003, the disclosure of which isincorporated by reference herein.

BACKGROUND ART

Biaxially oriented polyester films (for example, polyethyleneterephthalate films, which are commonly referred to as PET films) havewidely been used in the fields of insulating materials, drafting andphotographic films, magnetic tapes, vacuum metalized films and variouspackaging materials because they are excellent in electrical insulatingproperties, transparency, dimensional stability and toughness.

However, these biaxially oriented polyester films are insufficient inadhesion of the surface because molecular chains of the resinconstituting the films are highly oriented and are therefore inferior inadhesion to a printing ink, magnetic coating composition, depositedmetal or adhesive which is applied on the films.

In order to improve adhesion to the printing ink by activating thesurface of the polyester film, the surface of the films is commonlysubjected to a corona treatment, ultraviolet irradiation treatment,plasma treatment or flame treatment. Although adhesion can be improvedby these treatments, the activity deteriorates with time. Therefore,means for activation of the surface of these films is not necessarilysatisfactory.

As the other method of improving adhesion of the film surface, there issuggested an etching method of swelling or dissolving the surface usingchemicals such as acid, alkali, trichloroacetic acid and phenols. Thismethod enables decomposition and dissolution of crystal orientation inthe vicinity of the film surface and also deteriorates cohesivenessthereby to improve adhesion, thus ensuring the effect. However, some ofthese chemicals are harmful and involve some risk upon handling.

As a method similar to this method, there is suggested a method ofpreviously forming a thin coating layer (which is referred to as aprimer layer, anchor layer or undercoat layer) made of the material,which is different from that of a base material, on a film using acoating agent which is referred to as a primer coating agent or anchorcoating agent.

There has been used a method of applying a solvent-based coating agentprepared by dissolving in an organic solvent on a surface layer of afilm in the prior art, however, an aqueous coating agent (which isreferred to as an aqueous primer coating agent or aqueous anchor coatingagent) has commonly been used, recently, for reasons of safety andsanitation. Particularly, an aqueous polyurethane resin compositionhaving excellent adhesion to various base materials has been studied asthe aqueous coating agent.

Plastic films comprising a coating layer made of the aqueous coatingagent are used for various purposes. Among these plastic films, apolyester film is widely used as a food packaging film because of itsexcellent transparency and toughness. In these purposes, polyester filmis not usually used by itself and there is commonly used a laminatedfilm obtained by printing on a plastic film and laminating the plasticfilm with various films using an adhesive. Therefore, processabilityduring printing or lamination under various conditions as well asexcellent durability are required for the plastic film comprising thecoating layer formed thereon. Since various compositions such assolvent-based resin composition and aqueous resin composition are usedas the ink and adhesive to be coated on the coating layer formed on theplastic film, excellent solvent resistance, water resistance and heatresistance are required for the coating layer formed on the plasticfilm. To respond to these demands, the aqueous coating agent is commonlyused in combination with various crosslinking agents.

Recent diversification in the film has required various functions forthe film. Particularly, plastic films comprising a coating layer made ofpolyvinylidene chloride or a deposit layer made of aluminum formed forthe purpose of improving gas barrier performances of a packagingmaterial are used as a composition of the packaging material. In thatcase, a method of previously applying a coating agent on the surface ofa plastic to form a coating layer is used for the purpose of improvingadhesion to the layer made of polyvinylidene chloride or aluminumdeposit. To impart excellent gas barrier performances, such a coatinglayer must be uniformly formed. This requires that the coating agent canbe applied to various coating methods and can always form a uniformcoating layer even under various conditions.

As the method of applying a coating agent on the plastic film, there areemployed an in-line coating method of applying a coating agent duringthe biaxial stretching step in the manufacturing process of a plasticfilm and performing the lateral stretching step, and an off-line coatingmethod of applying a coating agent to the taken-up plastic filmperforming the biaxial stretching step, and drying the coating agent toform a coating layer.

In the in-line coating method, since the coating agent is applied beforecrystal orientation is completed during the biaxial stretching step ofthe plastic film, adhesion between the base film and the coating layeris improved. In case of a PET film, the stretching step is furtherperformed at the temperature of 150° C. or higher after applying thecoating agent. In that case, reaction with the coating agent andcrosslinking agent is so fast, and the coating layer cannot conform tothe base material during the stretching step, and thus cracking occursin the coating layer.

In the off-line coating method, since dimensional stability of the basematerial must be maintained, the drying step is commonly performed at alow temperature of 100° C. or lower. Therefore, a solvent-based coatingagent capable of forming a hard and uniform coating layer at lowtemperature was used. However, it is not preferable in view of safetyand problems such as environmental pollution and thus it is required todevelop an aqueous coating agent which can also be applied to theoff-line coating method.

Various suggestions have been made as a measure to counter theseproblems.

For example, there is disclosed that an aqueous resin compositioncomprising an aqueous polyester-urethane resin having a pendant carboxylgroup neutralized with ammonia or organic amine in a high-molecularweight compound obtained from a polyester polyol having an aromaticcyclic structure and a polyisocyanate compound can provide a primercoating agent which is excellent in water resistance and blockingresistance (see, for example, Patent Document 1).

According to this method, a hard aqueous polyurethane resin can beobtained by using a polyester having an aromatic cyclic structure.Because of high glass transition temperature of a polyurethane resin,the film forming process at high temperature is required in order toobtain a uniform coating layer.

Actually, various crosslinking agents are often used in combination forthe purpose of improving solvent resistance and heat resistance of thecoating layer. In that case, there arises a problem that an uniformcoating layer is hardly formed because of poor conformability to thebase material during the stretching step of the film in the in-linecoating method.

For the purpose of solving such a problem and forming a uniform coatinglayer, there is employed a method of plasticizing a resin as a maincomponent in a coating agent by using an organic solvent having a highboiling point as a film forming agent.

In the method of using the film forming agent, for example, there issuggested a polyurethane emulsion coating agent composition wherein MFT(Minimum Film Forming Temperature) is lowered and film formingproperties at normal temperature or lower temperature are improved byusing an oxyalkylene glycol derivative having a boiling point of 80 to270° C., which is a hydrophilic fusing agent, as the film forming agent(see, for example, Patent Document 2).

There is suggested a vacuum metalized polypropylene film whereinadhesion to a base material is improved by using a water-soluble organicsolvent such as N-methyl-2-pyrrolidone as a film forming agent andmixing it with a polyester-urethane resin (see, for example, PatentDocument 3).

However, these methods using the organic solvent have problems, forexample, harmfulness to the human body and poor safety such asinflammation, and therefore it is required to develop a coating agentwhich contains no organic solvent and is excellent in film formingproperties at lower temperature. Also in case of modifying the surfaceof plastic films having poor adhesion such as polypropylene, nylon andpolyester films, it has been required to develop a coating agent whichis excellent in adhesion between the coating agent and the basematerial.

When using the organic solvent as the film forming agent, there arises aproblem that the film forming agent remains in the coating film and thussurface hardness decreases and wear resistance and blocking resistancedeteriorate in case drying conditions at comparatively low temperatureof 100° C. or lower are required, like the off-line coating method, andalso there arises a problem that the water resistance deteriorates ifthe coating film is not sufficiently dried because the film formingagent has high hydrophilicity.

As the method of improving adhesion while maintaining heat resistance,there is suggested an aqueous polyurethane dispersion which is obtainedby adding a polymer for improving adhesion to a polyurethane resin anddispersing the mixture in water (see, for example, Patent Document 4).

In this aqueous dispersion, a trial of improving adhesion and heatresistance is made by adding a resin having a softening temperature of80 to 130° C., as a polymer for improving adhesion, to a polyurethaneresin. When the aqueous dispersion by means of such a method is appliedto the in-line coating method, conformability to the base materialduring the stretching step deteriorates, and thus it is difficult toobtain a uniform film free from coating film defects. When applied tothe off-line coating method at lower processing temperature, the aqueousdispersion has poor film forming properties, and thus it is difficult toobtain a uniform film free from coating film defects.

-   (Patent Document 1) Japanese Patent Application, Second Publication    No. Hei 8-22900 (page 1, left column to page 2, right column)-   (Patent Document 2) Japanese Patent Application, Second Publication    No. Sho 63-14748 (page 1, left column to page 2, right column)-   (Patent Document 3) Japanese Patent Application, First Publication    No. 2000-108262 (page 2, left column, claim 1 to page 2, right    column, paragraph “0005“)-   (Patent Document 4) Japanese Patent Application, First Publication    No. Hei 5-230364 (page 1, left column to page 2, right column)

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an aqueous coatingagent which has excellent film forming properties without using a filmforming agent comprising an organic solvent even when applied at acomparatively low temperature such as normal temperature, and also canform a coating layer which is excellent in adhesion to a base material,especially a polyester film.

Another object of the present invention is to provide an aqueous coatingagent capable of forming a coating layer which is excellent inconformability to film deformation and does not cause cracking duringthe following stretching step even when applied during the filmstretching step in the in-line coating method where processing isperformed at high temperature of 150° C. or higher.

The present inventors have intensively studied so as to achieve theabove objects and found that film forming properties during theapplication at comparatively low temperature can be improved and goodfilm forming properties can be obtained in the off-line coating methodby using an aqueous coating agent comprising a water-dispersiblepolyurethane resin having an aromatic cyclic structure, a waterdispersion prepared by dispersing resin particles containing a polyesterpolyol or polyether polyol, which is liquid at normal temperature, inwater, and a crosslinking agent capable of reacting with a hydroxylgroup.

By using a polyester polyol or polyether polyol having an aromaticcyclic structure in the molecule as the polyester polyol or polyetherpolyol which is liquid at normal temperature, adhesion to a polyesterfilm could be improved.

It has been found that the coating layer formed in the followingstretching step is excellent in conformability to film deformation evenwhen the coating agent is applied during the film stretching step, whichis usually performed, in the in-line coating method by means of such amethod, and thus good coating layer is obtained without causingcracking.

It is considered that such an effect of improving film formingproperties at low temperature contributes to the fact that thewater-dispersible polyurethane resin having an aromatic cyclic structureis plasticized by the polyester polyol or polyether polyol having anaromatic cyclic structure, which is liquid at normal temperature.However, the present inventors have confronted such a problem that, whena polyester polyol having an aromatic cyclic structure, which is liquidat normal temperature, is added in the water dispersion in the amountenough to exert the effect of improving film forming properties at lowtemperature, heat resistance deteriorates, resulting in poor blockingresistance.

The present inventors have further studied so as to solve the problemand found that good film forming properties and heat resistance do notdeteriorate by the use of a polyester polyol, which itself has not waterdispersibility but has hydrophobicity, as the polyester polyol having anaromatic cyclic structure, which is liquid at normal temperature and isto be added in a water dispersion, even when the amount to be added inthe water dispersion is small.

It is considered that, when using a polyester polyol havinghydrophobicity as the polyester polyol having an aromatic cyclicstructure, the polyester polyol having an aromatic cyclic structure isincorporated into dispersed particles formed from the water-dispersiblepolyurethane resin, which stably exists in water, and exists in the formof being covered with the layer of the water-dispersible polyurethaneresin. It is estimated that this exerts an influence on the fact thatthe effect of improving film forming properties at low temperature canbe obtained even when the amount of the polyester polyol having anaromatic cyclic structure decreases.

At the beginning, we considered that film forming properties at lowtemperature can be improved more effectively by bonding both ofwater-dispersible polyurethane resin and the polyester polyol having anaromatic cyclic structure by means of a chemical bond in case of formingdispersed particles containing both of them, and studied. However, filmforming properties at lower temperature could be improved when nochemical bond is formed between them.

The present inventors have found that adhesion to the base material suchas polyester film is also improved by such a method and the coatinglayer thus formed is noticeably excellent in conformability to filmdeformation and is also excellent in heat resistance, water resistance,solvent resistance and transparency even when applied to the in-linecoating method, and thus the present invention has been completed.

The present invention provides an aqueous coating agent comprising awater dispersion (C) prepared by dispersing resin particles containing awater-dispersible polyurethane resin (A) and at least one compoundselected from a hydrophobic polyester polyol (B-1) and a hydrophobicpolyether polyol (B-2) in water, and a crosslinking agent (D) capable ofreacting with a hydroxyl group, wherein the water-dispersiblepolyurethane resin (A) is obtained by reacting a polyester polyol (a-1),which is obtained by condensing a dicarboxylic acid containing anaromatic dicarboxylic acid as a main component with a polyol, with apolyisocyanate, and also contains 15 to 35% by weight of an aromaticcyclic structural unit based on the weight of the water-dispersiblepolyurethane resin (A), and wherein the hydrophobic polyester polyol(B-1) and/or the hydrophobic polyether polyol (B-2) are liquid at normaltemperature and contain 20 to 50% by weight of an aromatic cyclicstructural unit based on the weight of the hydrophobic polyester polyol(B-1) and/or the hydrophobic polyether polyol (B-2).

The term “hydrophobic” is generally understood that a certain substancehas such a property as weak interaction with water and weak affinitywith water. However, the term “hydrophobic” as used herein means that acertain substance itself has a property which is not dispersible orsoluble in water.

The term “liquid at normal temperature” as used herein means that it isliquid at 25° C.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the invention will be described indetail.

The aqueous coating agent of the present invention comprises a waterdispersion (C) prepared by dispersing resin particles containing awater-dispersible polyurethane resin (A) and a hydrophobic polyesterpolyol (B-1) and/or a hydrophobic polyether polyol (B-2) in water, and acrosslinking agent (D) capable of reacting with a hydroxyl group.

It is preferable to substantially form no chemical bond between thewater-dispersible polyurethane resin (A) and the hydrophobic polyesterpolyol (B-1) or the hydrophobic polyether polyol (B-2) contained in theresin particles because the water-dispersible polyurethane resin (A) canbe effectively plasticized and the effect of improving film formingproperties at low temperature exerted by the present invention can befurther enhanced.

The water-dispersible polyurethane resin (A) having an aromatic cyclicstructure used in the present invention will now be described.

The water-dispersible polyurethane resin (A) used in the presentinvention preferably has an aromatic cyclic structure and preferablyhas, as a hydrophilic group for imparting water dispersibility, ananionic group such as carboxyl group or sulfonic acid group or a saltthereof in the molecule.

The water-dispersible polyurethane resin (A) can be obtained by using apolyester polyol (a-1), which is obtained by condensing a dicarboxylicacid containing an aromatic dicarboxylic acid as a main component with apolyol, and a polyisocyanate as an essential component, optionally usingthe other polyol and polyamine as a chain extender, and reacting themaccording to a conventionally known method. As described in detailhereinafter, an anionic group can be introduced into the resultingwater-dispersible polyurethane resin (A) by using at least one kindhaving an anionic group among the polyester polyol (a-1) and the otherpolyol and polyamine.

The content of the anionic group in the water-dispersible polyurethaneresin (A) has a strong correlation with the particle size after thewater-dispersible polyurethane resin (A) was formed into a waterdispersion. In order to adjust the particle size within a proper range,the content of the anionic group is preferably adjusted within a rangefrom 50 to 1000 mmol/kg based on the water-dispersible polyurethaneresin (A). When the content is within the above range, it is madepossible to obtain good dispersion stability of resin particles withoutdeteriorating water resistance because the dispersed resin particlescause neither cohesion nor deposition after storage for a long periodand are stable.

A conventionally known method can be employed as the method ofintroducing the anionic group into the water-dispersible polyurethaneresin (A).

For example, there can be employed:

(i) a method of reacting a polyol containing a polyol having an anionicgroup such as carboxyl group or sulfonic acid group or a salt thereof asan essential component (the polyol having an anionic group may be eithera polyester polyol (a-1) or the other polyol which is optionally used)with a polyisocyanate to produce a water-dispersible polyurethane resin(A),

(ii) a method of reacting the polyol with the polyisocyanate under theconditions so that an isocyanate group of the polyisocyanate is presentin excess to a hydroxyl group of the polyol in (i) to produce aprepolymer having an isocyanate group, and reacting the prepolymer witha low-molecular weight polyol and polyamine, thereby to perform chainextension (increase in molecular weight) to produce a water-dispersiblepolyurethane resin (A) having an anionic group, and

(iii) a method of using a polyol (polyester polyol (a-1) having noanionic group, optionally the other polyol), reacting the polyol withthe polyisocyanate under the conditions so that an isocyanate group ofthe polyisocyanate is present in excess to a hydroxyl group of thepolyol to produce a prepolymer, and reacting the prepolymer with alow-molecular weight polyol and polyamine having an anionic group,thereby to perform chain extension (increase in molecular weight) toproduce a water-dispersible polyurethane resin (A) having an anionicgroup.

In case the water-dispersible polyurethane resin (A) has a carboxylgroup and/or a sulfonic acid group as the anionic group, good waterdispersibility can be imparted by neutralizing a portion or all of them.In that case, there can also be used at least one neutralizer selectedfrom the group consisting of organic amines such as ammonia,triethylamine, pyridine, and morpholine; alkanolamines such asmonoethanolamine, and metal base compounds containing Na, K, Li, and Ca.The neutralization rate is preferably within a range from 0.5 to 3.0(molar ratio), and more preferably from 0.9 to 2.0 (molar ratio), interms of a ratio of a neutralizer to an anionic group. When theneutralization rate is within the above range, table waterdispersibility can be imparted without deteriorating water resistance.

Typical examples of the polyol having a carboxyl group, which can beused as the polyol having an anionic group in the method (i) or (ii),include 2,2′-dimethylolpropionic acid, 2,2′-dimethylolbutanoic acid,2,2′-dimethylolbutyric acid, and 2,2′-dimethylolvaleric acid. Carboxylgroup-containing polyester polyols, which can be obtained by reactingthese polyols having a carboxyl group with various polycarboxylic acids,can also be used.

Typical examples of the polyol having a sulfonic acid group, which canbe used as the polyol having an anionic group in the method (i) or (ii),include polyester polyols having an aromatic sulfonic acid group or asalt thereof obtained by reacting a dicarboxylic acid such as5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid,or 5[4-sulfophenoxy]isophthalic acid, or a sulfonate of the dicarboxylicacid and at least one kind selected from the group consisting of metalions such as Na, K, Li and Ca ions, ammonia, diethylamine, andtriethylamine, with various polyols.

In addition to the polyol having an anionic group, there can also beused a nonion group-containing polyol such as polyalkylene glycol havinga number-average molecular weight of 300 to 10,000, which contains atleast 30% by weight of a repeating unit of ethylene oxide and also hasat least one active hydrogen atom-containing group. The content of thenonionic group is preferably adjusted to 10% by weight or less based onthe entire water-dispersible polyurethane resin (A). When the content iswithin the above range, good water dispersion stability can be obtainedwithout deteriorating water resistance.

The polyester polyol (a-1) obtained by condensing the dicarboxylic acidcontaining an aromatic dicarboxylic acid as a main component with thepolyol, which is used in the production of the water-dispersiblepolyurethane resin (A), will now be described. Such a polyester polyol(a-1) can be produced by a conventionally known method usingconventionally known various dicarboxylic acids and polyols.

Examples of the aromatic dicarboxylic acid, which can be used in theproduction of the polyester polyol (a-1), include aromatic dicarboxylicacids such as terephthalic acid, isophthalic acid, orthophthalic acid,1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylicacid, and 1,2-bis(phenoxy)ethane-P,P′-dicarboxylic acid, and acidanhydride or ester forming derivatives thereof; aromatichydroxycarboxylic acids such as p-hydroxybenzoic acid, and ester formingderivatives thereof; and sulfonic acid group-containing aromaticdicarboxylic acids such as 5-sulfoisophthalic acid, and ester formingderivatives thereof.

In addition to these aromatic dicarboxylic acids, aliphatic carboxylicacids and alicyclic carboxylic acids can also be used. Examples thereofinclude aliphatic dicarboxylic acids such as succinic acid, succinicanhydride, adipic acid, suberic acid, azelaic acid, sebacic acid, dimeracid, maleic anhydride, and fumaric acid; alicyclic dicarboxylic acidssuch as 1,4-cyclohexanedicarboxylic acid; and anhydrides or esterforming derivatives thereof. These compounds may be used in combination.

Examples of the polyol, which can be used in the production of thepolyester polyol (a-1), include polyols having an aromatic cyclicstructure, such as bisphenol A, bisphenol S, hydroquinone,bishydroxyethoxybenzene, or alkylene oxide adducts thereof; aliphaticdiols such as ethylene glycol, propylene glycol, 1,3-propanediol,1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,neopentyl glycol, diethylene glycol, triethylene glycol, tetraethyleneglycol, dipropylene glycol, tripropylene glycol, polyethylene glycol,3-methyl-1,5-pentanediol, and 2-butyl-2-ethyl-1,3-propanediol; alicyclicdiols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, andhydrogenated bisphenol A; and polyols as a polyfunctional component,such as glycerin, trimethylolpropane, and pentaerythritol.

There can also be used aliphatic polyols obtained by ring-openingpolymerization of a cyclic ester such as ε-caprolactone orγ-valerolactone in the presence of the above polyol and catalyst.

These aliphatic polyols may be used alone or in combination.

The polyester polyol (a-1) preferably has a hydroxyl value within arange from 10 to 350, and the hydroxyl value is particularly preferablywithin a range from 20 to 300. When the hydroxyl value is within theabove range, the resulting polyurethane resin has a high cohesion energyand also the aqueous coating agent obtained by using the polyesterpolyol is excellent in solvent resistance, water resistance and blockingresistance.

In the production of the water-dispersible polyurethane resin (A) usedin the present invention, it is preferable to use a polyester polyolobtained by condensing a dicarboxylic acid containing an aromaticdicarboxylic acid as a main component with a polyol, terephthalic acidand/or isophthalic acid accounting for 70 to 100 mol % of the totalamount of the dicarboxylic acid, among the polyester polyol (a-1). Byusing such a polyester polyol, it is made possible to provide an aqueouscoating agent capable of forming a coating layer which is excellent inadhesion to a base material, especially a polyester film, and is alsoexcellent in heat resistance such as blocking resistance, waterresistance, solvent resistance, and transparency.

In the production of the water-dispersible polyurethane resin (A) usedin the present invention, polyols other than the above-describedpolyester polyol (a-1) can be used as long as adhesion to base materialand blocking resistance are not adversely affected.

Examples of the polyol include polyester polyol, polyether polyol, andpolycarbonate polyol. These polyols may be used alone or in combination.It is particularly preferable to mainly use a polyester polyol in viewof excellent adhesion to various base materials and cost.

The polyester polyol can be produced by reacting the aliphaticcarboxylic acid or alicyclic carboxylic acid, which was described asthose used in the production of the polyester polyol (a-1), with variouspolyols according to a conventionally known method.

In this case, monoalcohols such as methanol, ethanol, n-butanol,isopropanol, and n-hexanol may be used in combination as long as anincrease in molecular weight of the water-dispersible polyurethane resin(A) is not adversely affected.

As described above, there can be employed a method of previouslyreacting the polyester polyol (a-1) and, optionally, the other polyolwith various polyisocyanates under the conditions so that an isocyanategroup of the polyisocyanate is present in excess to a hydroxyl group ofthe entire polyol, in the production of the water-dispersiblepolyurethane resin (A), to produce a prepolymer having an isocyanategroup, and reacting the prepolymer with a low-molecular weight polyoland polyamine, thereby to perform chain extension to increase themolecular weight.

In this case, as the low-molecular weight polyol, there can be usedpolyols having a carboxyl group, such as 2,2′-dimethylolpropionic acid,2,2′-dimethylolbutanoic acid, 2,2′-dimethylolbutyric acid, and2,2′-dimethylolvaleric acid; aliphatic diols such as ethylene glycol,propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, dipropylene glycol,tripropylene glycol, polyethylene glycol, 3-methyl-1,5-pentanediol, and2-butyl-2-ethyl-1,3-propanediol; and alicyclic diols such as1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and hydrogenatedbisphenol A. Furthermore, polyols such as glycerin, trimethylolpropane,and pentaerythritol can also be used as the polyfunctional component.

As the polyamine, there can be used polyamines having an anionic group,for example, diaminosulfonate such as metal salt ofN-(2-sulfoethyl)ethylenediamine or2-(β-aminoalkyl-aminopropionamide)-alkane sulfonate, and an adduct of analiphatic primary diamine such as ethylenediamine and α-an olefincarboxylic acid such as (meth)acrylic acid; and polyamines having noanionic group, for example, diamines such as 1,2-diaminoethane, 1,2-or1,3-diaminopropane, 1,2- or 1,3- or 1,4-diaminobutane,1,5-diaminopentane, 1,6-diaminohexane, piperazine,N,N′-bis-(2-aminoethyl)piperazine,1-amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane(isophoronediamine),bis-(4-aminocyclohexyl)methane, bis-(4-amino-3-butylcyclohexyl)methane,and 1,2-, 1,3- or 1,4-diaminocyclohexane or 1,3-diaminopropane,polyamine such as diethylenetriamine or triethylenetetramine, andhydrazine or hydrazine derivatives such as dihydrazide adipate.

Furthermore, amino alcohols having both an amino group and an alcoholichydroxyl group in the molecule can also be used and examples thereofinclude ethanolamine, N-methyldiethanolamine, propanolamine,N-methyldiisopropanolamine, N-ethyldiethyleneamine,N-ethyldiisopropanolamine, aminoethylethanolamine, and diethanolamine.

As the polyamine, a polyamine having the number of functional groups of2 or more is preferably used so as not to adversely affect durability.In this case, a polyamine having the number of functional groups of 2 ormore may be used alone, or two or more kinds of polyamines may be usedto adjust the number of functional groups to 2 or more.

In case the molecular weight is increased by chain extension of theprepolymer having an isocyanate group, the amount of the polyamine ispreferably 1.9 equivalents or less, and more preferably from 0.6 to 1.0equivalents, per equivalent of the isocyanate group. When chainextension is performed by using the polyamine in the amount within theabove range, the resulting aqueous coating agent is excellent indurability and light fastness.

The polyisocyanate, which is used in the production of thewater-dispersible polyurethane resin (A) used in the present invention,may be a conventionally known polyisocyanate.

For example, there can be used 1,4-tetramethylene diisocyanate,1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate,cyclohexane-1,3- or 1,4-diisocyanate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (anothername: isophorone diisocyanate, IPDI),dicyclohexylmethane-4,4′-diisocyanate (another name: hydrogenated MDI),2- or 4-isocyanatocyclohexyl-2′-isocyanatocyclohexylmethane, 1,3- or1,4-bis-(isocyanatomethyl)-cyclohexane,bis-(4-isocyanato-3-methylcyclohexyl)methane, 1,3- or1,4-α,α,α′,α′-tetramethylxylylene diisocyanate, 2,4- or2,6-diisocyanatotoluene, 2,2′-, 2,4′- or4,4′-diisocyanatodiphenylmethane (MDI), 1,5-naphthalene diisocyanate, p-or m-phenylene diisocyanate, xylylene diisocyanate, anddiphenyl-4,4′-diisocyanate.

Among these polyisocyanates, an aromatic diisocyanate is preferably usedin view of mechanical strength, and an aliphatic or alicyclicdiisocyanate compound is preferably used in view of durability and lightfastness.

As the organic solvent used in the production of the water-dispersiblepolyurethane resin (A), an organic solvent having a boiling point of150° C. or lower is preferably used in view of formation of fineparticles upon water dispersion, and removal of the residual solventcontained in the water dispersion (C) after distillation.

Examples of the organic solvent having a boiling point of 150° C. orlower include benzene, toluene, ethyl acetate, acetone, methyl ethylketone, diethyl ether, tetrahydrofuran, methyl acetate, acetonitrile,chloroform, and methylene chloride. These organic solvents can be usedalone or in combination. Among these organic solvents, acetone, methylethyl ketone and ethyl acetate are preferably used as the solvent havinghigh solubility to the water-dispersible polyurethane resin (A). For thepurpose of further enhancing water dispersibility, an alcohol solventsuch as methanol, ethanol or isopropyl alcohol may be used upon waterdispersion as long as an increase in molecular weight of thepolyurethane resin is not adversely affected.

The content of the urethane-bond unit (—NH—COO—) per 1000 g of thewater-dispersible polyurethane resin (A) is preferably within a rangefrom 1.0 to 4.0 mols.

As described above, a urea bond is formed when chain extension isperformed by reacting the prepolymer with the polyamine. In this case,the total of the content of the urethane-bond unit (—NH—COO—) and theurea bond unit (—NH—CO—NH—) per 1000 g of the water-dispersiblepolyurethane resin (A) is preferably within a range from 1.0 to 4.0mols.

When the total of the content is within the above range, a cohesionenergy of the polyurethane molecule increases and therefore theresulting coating layer has suitable hardness, and thus making possibleto improve solvent resistance, and heat resistance such as blockingresistance.

The content of the aromatic cyclic structural unit in thewater-dispersible polyurethane resin (A) is preferably within a rangefrom 15 to 35% by weight, and more preferably from 20 to 30% by weight.When the content is within the above range, the resulting aqueouscoating agent is particularly excellent in adhesion to polyester basematerial, solvent resistance, water resistance, and heat resistance suchas blocking resistance.

The number-average molecular weight of the water-dispersiblepolyurethane resin (A) is preferably within a range from 5000 to 50000,and more preferably from 6000 to 30000. When the number-averagemolecular weight is within the above range, the resulting aqueouscoating agent is excellent in solvent resistance, water resistance, andheat resistance such as blocking resistance.

The hydrophobic polyester polyol (B-1) and hydrophobic polyether polyol(B-2), which are liquid at normal temperature and also contain 20 to 50%by weight of an aromatic cyclic structural unit, used in the presentinvention will now be described.

The term “hydrophobic polyol (B)” as used herein means both ahydrophobic polyester polyol (B-1) and a hydrophobic polyether polyol(B-2).

Since the hydrophobic polyol (B) is liquid at normal temperature, itserves as a film forming agent and accelerates plasticization of thewater-dispersible polyurethane resin (A), thus making it possible toimprove film forming properties. To further enhance such an effect, itis preferable that the hydrophobic polyol (B) and the water-dispersiblepolyurethane resin (A) are not substantially chemically-bonded.

Although the hydrophobic polyol (B) itself has no water dispersibility,it is incorporated into dispersed particles formed from thewater-dispersible polyurethane resin (A), which stably exists in water,and exists in the form of being covered with the layer of thewater-dispersible polyurethane resin. It is estimated that this formmakes it possible to exert a preferable effect of improving film formingproperties at low temperature even when the amount of the hydrophobicpolyol (B) decreases.

The content of the hydrophilic group enough to make the hydrophobicpolyol (B) to be hydrophobic preferably satisfies the following both ofconditions: (1) 50 mmol/kg or less in case of an ionic group, and (2) 5%by weight or less in case of an ethylene oxide [(CH₂CH₂O)n: n ≧5]constituent unit having 5 or more repeating units. By using such ahydrophobic polyol (B), the resulting coating layer is excellent inwater resistance.

The hydrophobic polyester polyol (B-1) used in the present invention canbe produced by a conventionally known method using conventionally knownvarious dicarboxylic acids and polyols. However, any of the abovedicarboxylic acids and polyols must have an aromatic cyclic structure.

As the aromatic dicarboxylic acid which can be used in the production ofthe hydrophobic polyester polyol (B-1), the aliphatic carboxylic acid,the alicyclic carboxylic acid and the polyol having an aromatic cyclicstructure which can be used in combination with the aromaticdicarboxylic acid, and the aliphatic polyol and the alicyclic polyolwhich can be used in combination with the aromatic dicarboxylic acid,for example, there can be used those described in the production of thepolyester polyol (a-1), which is a raw material of the water-dispersiblepolyurethane resin (A), respectively.

In case of the hydrophobic polyester polyol (B-1), it is preferable thatat least one polycarboxylic acid selected from isophthalic acid andorthophthalic acid accounts for 60 mol % or more of the entiredicarboxylic acid to be used, while the polyol to be used is analiphatic polyol having 2 to 8 carbon atoms.

It is more preferable that orthophthalic acid accounts for at least 60mol % of the total amount of the dicarboxylic acid. By using such adicarboxylic acid, the resulting hydrophobic polyester polyol (B-1) haslow crystallinity and is liquid which is suited for use in the presentinvention.

It is more preferable that at least one polyol selected from the groupconsisting of ethylene glycol, diethylene glycol and triethylene glycolaccounts for 50 mol % or more of the entire polyol.

Consequently, the resulting hydrophobic polyester polyol (B-1) has lowcrystal orientation and is liquid at normal temperature, and also canplasticize the water-dispersible polyurethane resin (A) moreeffectively. Therefore, film forming properties at low temperature areimproved, and thus making it possible to form a markedly uniform coatinglayer when applied to the off-line coating method where drying isperformed at comparatively low temperature of 100° C. or lower, ordrying is performed at normal temperature.

The hydrophobic polyether polyol (B-2) can be produced by adding acyclic ether compound or cyclic carbonate compound such as alkyleneoxide to a polyol having various aromatic cyclic structures by means ofthe ring-opening polymerization reaction in the presence of a catalyst.A cyclic compound adduct of a polynuclear phenol compound, which isobtained by reacting a polynuclear phenol compound with a cycliccompound such as alkylene oxide described hereinafter in the presence ofa catalyst, is more preferable and a propylene oxide adduct of apolynuclear phenol compound is particularly preferable.

Examples of the polynuclear phenol compound include bisphenol compoundssuch as bisphenol A, bisphenol S, bisphenol F, bisphenol E, bisphenol Z,tetramethylbisphenol A, diallylbisphenol A, 4-4′-oxybisphenol, biphenol,tetramethylbiphenol, bisphenol fluorene, biscresol fluorene, and terpenediphenol; and novolaks such as phenol novolak, cresol novolak, xylylenenovolak, bisphenol A novolak, triphenylmethane novolak, biphenylnovolak, dicyclopentadienephenol novolak, and terpenephenol novolak, andthese polynuclear phenol compounds can be used alone or in combination.

Examples of the cyclic compound include cyclic ether compounds such asethylene oxide, propylene oxide, butylene oxide, oxetane, andtetrahydrofuran; and cyclic carbonate compounds such as ethylenecarbonate and propylene carbonate. These cyclic compounds can be usedalone or in combination.

As the hydrophobic polyether polyol (B-2), a propylene oxide adduct of abisphenol compound containing a constituent unit originating frompropylene oxide and a propylene oxide adduct of a phenol novolakcompound are preferable because they are liquid at normal temperature.In case of the hydrophobic polyether polyol, film forming properties atlow temperature are improved by enhancing the plasticization effect tothe water-dispersible polyurethane resin (A), and thus making itpossible to form a markedly uniform coating layer even when coating anddrying are performed at comparatively low temperature.

In this case, in view of compatibility with the water-dispersiblepolyurethane resin (A), those obtained by adding 2 to 60 mols ofpropylene oxide to 1 mol of the polyol having an aromatic cyclicstructure are preferable, and those obtained by adding 2.5 to 30 mols ofpropylene oxide to 1 mol of the polyol having an aromatic cyclicstructure are more preferable.

The number-average molecular weight of the hydrophobic polyol (B) ispreferably within a range from 200 to 4000, and more preferably from 250to 2000. When the number-average molecular weight is within the aboverange, the hydrophobic polyol (B) has low viscosity at normaltemperature and film forming properties at low temperature can beimproved by enhancing the plasticization effect to the water-dispersiblepolyurethane resin (A).

The hydroxyl value of the hydrophobic polyol (B) is preferably within arange from 20 to 500, and more preferably form 50 to 400. When thehydroxyl value and the number-average molecular weight of thehydrophobic polyol (B) are within the above range, reactivity with thecrosslinking agent (D) capable of reacting with a hydroxyl group isimproved and the crosslinking reaction proceeds without adverselyaffecting film forming properties at low temperature. Therefore, evenwhen applied during the film stretching step in the in-line coatingmethod where processing is performed at high temperature, it is madepossible to form a tough coating layer having excellent conformabilityto film deformation without causing cracking after the completion of thecrosslinking reaction, during the following stretching step, and thusmaking it possible to improve solvent resistance, water resistance, andheat resistance such as blocking resistance.

The hydrophobic polyester polyol (B-1) and the hydrophobic polyetherpolyol (B-2) may be used alone or in combination, respectively. Amongthese polyols, a hydrophobic polyester polyol (B-1) is preferable inview of adhesion to polyester base material and blocking resistance.

The content of the aromatic cyclic structural unit in the hydrophobicpolyol (B) is preferably within a range from 20 to 50% by weight, andmore preferably from 25 to 40% by weight.

When the content is within the above range, the coating film obtainedafter crosslinking is particularly excellent in adhesion to polyesterbase material, solvent resistance, water resistance, and heat resistancesuch as blocking resistance.

The method of producing the water dispersion (C), which is prepared bydispersing resin particles containing the water-dispersible polyurethaneresin (A) and the hydrophobic polyol (B) in water, used in the presentinvention will now be described.

Such a water dispersion (C) can be produced by using variousconventionally known methods, for example, the following methods (i) and(ii) in combination. (i) A water dispersion (C) can be obtained byuniformly mixing a water-dispersible polyurethane resin (A) with ahydrophobic polyol (B), neutralizing the mixture, adding water to themixture, thereby to emulsify and disperse the mixture, and optionallyperforming distillation. (ii) A prepolymer having a residual isocyanategroup is produced by reacting a polyester polyol (a-1) and, optionally,the other polyol with a polyisocyanate in an equivalent ratio of anisocyanate group to a hydroxyl group within a range from (1 to 3) to 1,and preferably from (1 to 2) to 1 in an organic aprotic solvent underthe conditions of a temperature within a range from 30 to 150° C., andpreferably from 50 to 120° C., using a one-shot method or a multi-stagemethod.

In this case, a prepolymer having an anionic group can be obtained byusing a polyol having a carboxyl group or a sulfonic acid group as thepolyol. In this case, the polyol having a carboxyl group or a sulfonicacid group may be either a polyester polyol (a-1), or the other polyolwhich is optionally used.

The resulting prepolymer is mixed with the hydrophobic polyol (B) andthen the mixture is uniformly melted. In this case, it is important tomaintain at 60° C. or lower so that the isocyanate group of theprepolymer does not react with the hydroxyl group of the hydrophobicpolyol (B).

After neutralizing the mixture, the mixture is emulsified and dispersedby adding water dropwise or introducing water by several portions. Inthis case, it is important to emulsify at 60° C. or lower so as to avoidthe side reaction with water.

Then, an aqueous solution containing a low-molecular weight polyol orpolyamine is added in the water dispersion in which the isocyanate groupis remained, thereby to perform chain extension (increase in molecularweight), and thus the objective water dispersion (C) is obtained. Anaqueous dispersion (C) with less harmfulness can be obtained byoptionally performing desolvation of the resulting water dispersion.

The mixing ratio of the water-dispersible polyurethane resin (A) to thehydrophobic polyol (B) used in the present invention, (A)/(B), ispreferably within a range from 95/5 to 50/50, and particularlypreferably from 90/10 to 70/30 in terms of a weight ratio. When themixing ratio is within the above range, it is made possible to stablyform particles without deteriorating water dispersibility. Since thewater-dispersible polyurethane resin (A) is appropriately plasticized bythe hydrophobic polyol (B) and the resulting aqueous coating agent isexcellent in film forming properties at low temperature andconformability to base material, it is made possible to form a goodcoating layer without causing coating film defects even when applied toeither the in-line coating method or the off-line coating method.

The crosslinking agent (D) capable of reacting with a hydroxyl groupused in the present invention will now be described.

The crosslinking agent (D) is used to improve heat resistance such asblocking resistance, wet heat resistance and solvent resistance of thecoating layer formed by using the aqueous coating agent of the presentinvention. As the crosslinking agent (D), for example, amino resin andpolyisocyanate can be used. The polyisocyanate is preferably apolyisocyanate which contains polyoxyethylene and a hydrophilic group,and also has water solubility or water dispersibility.

When the crosslinking agent (D) is mixed with the water dispersion (C)used in the present invention, it reacts with the hydrophobic polyesterpolyol (B-1) or the water-dispersible polyurethane resin (A) at normaltemperature with a lapse of time, and also the crosslinking agent (D)itself causes self-condensation. Therefore, it is not preferable thatthe crosslinking agent is stored for a long time after mixing with thewater dispersion (C). Although the pot life varies depending on the kindof the crosslinking agent (D), the aqueous coating agent of the presentinvention is preferably prepared by mixing the crosslinking agent (D)with the water dispersion (C) according to a conventionally known methodimmediately before applying to the base material. When using apolyisocyanate as the crosslinking agent (D), the polyisocyanate ispreferably used as soon as possible after mixing with the waterdispersion (C).

The amount of the crosslinking agent (D) is preferably within a rangefrom 1 to 20% by weight, and more preferably form 3 to 10% by weight,based on the water-dispersible polyurethane resin (A) and thehydrophobic polyol (B) of the present invention. When the amount iswithin the above range, it is made possible to improve heat resistancesuch as blocking resistance, wet heat resistance and solvent resistanceof the resulting coating layer without adversely affecting adhesion tobase material and conformability.

These crosslinking agents (D) can be used in combination and also curingaccelerators can be used. Crosslinking agents such as epoxy compound,carbodiimide, aziridine compound and oxazoline compound can also beused.

The aqueous coating agent of the present invention can contain aqueousacrylic resins, aqueous polyester resins and SBR latex resin(styrene-butadiene rubbers) as long as adhesion to base material andfilm forming properties at low temperature are not adversely affected.The coating agent preferably contains these resins in the amount of 30%by weight or less, and more preferably 10% by weight or less in terms ofthe solid content.

If necessary, the aqueous coating agent of the present invention canfurther contain inorganic fine particles (colloidal silica) forimproving blocking resistance or slip resistance; alcohols (ethanol andisopropyl alcohol) for improving wettability; anionic, nonionichydrocarbon or fluorine surfactants; acetylene glycol leveling agents“SURFYNOL” (manufactured by Air Products Co.); and polyalkyleneglycol-modified polysiloxanes such as BYK-348, 346, 345 and 341(manufactured by BYK-Chemie GmbH). Among these additives, acetyleneglycol leveling agents are preferably used to improve wettability.Auxiliaries such as antistatic agents can also be blended.

After adjusting to any resin concentration, the aqueous coating agent ofthe present invention can be applied on a base material byconventionally known coating methods such as gravure coating method, rodcoating method, spray coating method, air knife coating method, and rollcoating method.

In this case, the concentration of the resin in the aqueous coatingagent is preferably adjusted within a range from 0.1 to 40% by weight.

In this case, the thickness of the coating layer is preferably within arange from 0.01 to 100 μm, and more preferably from 0.05 to 50 μm. Whenthe thickness is within the above range., the surface of the basematerial can be modified without adversely affecting characteristics ofthe base material.

The aqueous coating agent of the present invention is excellent inadhesion to textiles, synthetic leathers, artificial leathers, naturalleathers, metals (aluminum, iron, copper), rubbers, glasses, papers, andlumbers, and its dry film is excellent in water resistance and blockingresistance. Therefore, the aqueous coating agent of the presentinvention is can be used in the fields of treating agents for fibers andleather base materials, and aqueous coating agents and is thereforeextremely useful.

Furthermore, the aqueous coating agent of the present invention canexert various performances described above even when applied toplastics. As the plastic, a biaxially stretched plastic film can beused. To further enhance the effect of the present invention, theaqueous coating agent is preferably applied during the biaxialstretching step of the plastic film, i.e. before the completion of thebiaxial stretching treatment.

Preferable examples of the film made of plastics, on which the aqueouscoating agent of the present invention is applied, include vinylchloride resin, vinylidene chloride resin, polyamide resin (nylon),polyolefin resin (polyethylene resin, polypropylene resin), polyesterresin, unsaturated polyester resin, polyurethane resin, polystyreneresin, acrylic resin, ethylene-vinyl acetate copolymer,polyvinyl-alcohol polymer, and ethylene-vinyl alcohol copolymer. Amongthese plastics, a polyester resin and a polyamide resin are particularlypreferable.

Examples of the polyester resin include polyalkylene terephthalate as amain component, such as polyethylene terephthalate, polybutyleneterephthalate or polyethylene naphthalate, and the polyester resin maybe in the form of a film, a sheet, and a molded article. It furtherincludes those obtained by copolymerization of other aromaticdicarboxylic acids such as isophthalic acid and2,6-naphthalenedicarboxylic acid, or mixtures thereof, and thesematerials may be in the form of a film, a sheet, and a molded article.

Examples of the polyamide resin include nylon 6 (polycaproamide), nylon66 (polyhexamethyleneadipamide), nylon 610 (polyhexamethylenesebacamide), nylon 11 (polyundecanamide), nylon 12 (polylauroamide),methaxylylenediamine nylon, copolymers, modified products and mixturesthereof, and these materials may be in the form of a film, a sheet, anda molded article.

The aqueous coating agent of the present invention can be preferablyused as surface modifiers for plastic films, but is more preferably usedas primer coating agents and anchor coating agents which are used forthe purpose of improving adhesion of the surface of plastic films.

The aqueous coating agent of the present invention can also serve aseffective aqueous primer coating agents and aqueous anchor coatingagents to plastics which are not subjected to a surface treatment. Tofurther enhance the effect, it is preferable to use plastics which arepreviously subjected to physical and chemical treatments, such as coronatreatment and alkali treatment.

The aqueous coating agent of the present invention has processability ina wide temperature range and excellent adhesion to base material and isalso excellent in blocking resistance, water resistance and solventresistance, and is therefore applied to not only the in-line processingmethod, but also to the off-line processing method. Thus, the aqueouscoating agent of the present invention can be widely used in the fieldssuch as food packaging films, gas-barrier films and vaccum metalizedfilms.

EXAMPLES

The present invention will be described in detail by the examples, butis not limited to the following examples. In the examples, parts andpercentages are by weight unless otherwise specified. The procedures forevaluation of various properties are as follows. The present inventionis not limited to the following respective examples and constituentfeatures of these examples may be appropriately combined.

[Preparation of Aqueous Coating Agents A and B]

To an aqueous solution prepared by diluting 100 parts of each of waterdispersions obtained in the Examples and Comparative Examples describedhereinafter with 100 parts of water, 2 parts of AQANATE 100(isocyanurate compound of hexamethylene diisocyanate having apolyethylene glycol side chain, manufactured by NIPPON POLYURETHANEINDUSTRY CO., LTD.) was added and the mixture was sufficiently stirredso as to uniformly disperse the isocyanurate compound to obtain anaqueous coating agent A.

To an aqueous solution prepared by diluting 100 parts of each of waterdispersions obtained in the Examples and Comparative Examples describedhereinafter with 100 parts of water, 5 parts of BECKAMINE APM(trimethylolmelamine resin, manufactured by DAINIPPON INK & CHEMICALSCo., Ltd.) was added and the mixture was sufficiently stirred so as touniformly disperse the trimethylolmelamine resin to obtain an aqueouscoating agent B.

[Procedure for Evaluation of Film Forming Properties]

1 g of the aqueous coating agent B prepared as described above wastransferred onto a metal laboratory dish having a diameter of 65 mm andthen uniformly diluted by adding 4 g of water to obtain a sample, whichwas dried under the conditions of a temperature of 5° C. or 20° C. and arelative humidity of 50% for 24 hours to form a film. The surfaceconditions of the resulting film were visually observed and thenevaluated by the following three-rank rating system.

-   A: uniform film was formed-   B: film was formed with cracking-   C: formed into powder without forming film    [Production of Coating Film]

On a base film (PET: 12 μm, OPP (oriented polypropyrene): 15 μm), eachaqueous coating agent prepared above was applied in a dry thickness ofabout 0.3 μm, and then heat-treated and cured under the followingconditions to obtain a surface-treated film.

Aqueous coating agent A: It was heat-treated at 80° C. for 60 secondsand then cured at a temperature of 23° C. and a relative humidity of 65%for 2 days.

Aqueous coating agent B: It was heat-treated at 150° C. for 5 minutesand then cured at a temperature of 23° C. and a relative humidity of 65%for 2 days.

[Adhesion to Base Material <Cellophane Adhesive Tape Peeling Test>]

The surface-treated film (PET, OPP) obtained above was subjected to apeeling test using an adhesive tape having a width of 24 mm manufacturedby NICHIBAN CO., LTD., and then the results were evaluated by thefollowing five-rank rating system.

-   1: week adhesive force, completely peeled-   2: 50% or more of sample was peeled-   3: 10 to 50% of sample was peeled-   4: considerably strong adhesive force, only less than 10% of sample    was peeled-   5 very adhesive force, not peeled    [Test of Conformability to Base Material]

After stretching the surface-treated OPP film obtained by using theaqueous coating agent B by hand, the surface conditions of the coatinglayer were observed and the results were evaluated by the followingthree-rank rating system.

-   A: cracking did not occur-   B: cracking slightly occurred, no peeling of coating layer-   C: cracking occurred, coating layer was completely peeled from film    [Blocking Resistance]

After laminating the treated surfaces of the surface-treated filmobtained by using the aqueous coating agent B with each other, the filmwas allowed to stand under a load of 100 g/cm² in an atmosphere at atemperature of 40° C. and a relative humidity of 65% for 24 hours andthe film was peeled. Adhesion was evaluated by the following three-rankrating system.

-   A: no adhesion, easily peelable-   B: some adhesion, no change in coated surface-   C: surface defects of some coated surface were caused by adhesion    [Solvent Resistance]

After rubbing the coating layer of the surface-treated PET film obtainedby using the aqueous coating agent B using a cotton bar impregnated withethyl acetate, the number of rubbings until the coating layer wasremoved and the base material layer appears was evaluated by thefollowing five-rank rating system.

-   1: less than 10%-   2: 10 to 20-   3: 20 to 30-   4: 30 to 40-   5: 50 or more    [Water Resistance]

After dipping the surface-treated PET film obtained by using the aqueouscoating agent B in warm water at 40° C. for 24 hours, a peeling testusing a cellophane adhesive tape was performed.

[Adhesion to Ink]

On the surface-treated PET film obtained by using the aqueous coatingagent B, a gravure ink was applied in a dry thickness of about 10 μmusing a bar coater, dried at 80° C. and aged at 60° C. for one day.Then, a peeling test using a cellophane adhesive tape was performed. Theresults were evaluated by the following five-rank rating system.

-   1: very week adhesive force, completely peeled-   2: 50% or more of sample was peeled-   3: 10 to 50% of sample was peeled-   4: considerably strong adhesive force, only less than 10% of sample    was peeled-   5: very adhesive force, not peeled-   Gravure ink used for evaluation-   “CLS-709 White” (gravure ink for cellophane printing, manufactured    by DAINIPPON INK & CHEMICALS Co., Ltd.): 50 parts mixed solvent of    toluene/ethyl acetate/methyl ethyl ketone=1/1/1 (weight ratio): 100    parts    <Preparation of Polyester Polyol for Preparation of    Water-Dispersible Polyurethane Resin (A)>

In a reaction vessel equipped with a thermometer, a nitrogen gasintroducing tube and a stirrer, 830 parts of terephthalic acid, 830parts of isophthalic acid, 374 parts of ethylene glycol, 598 parts ofneopentyl glycol and 0.5 parts of dibutyltin oxide were charged whileintroducing a nitrogen gas and the polycondensation reaction wasperformed at 230° C. for 15 hours until the acid value became 1 or lessat 180 to 230° C. to obtain a polyester polyol P-1 having a hydroxylvalue of 74.5 and an acid value of 0.2.

According to the formulation shown in Table 1, a polyester polyol P-3was obtained by the same procedure as described above.

In a reaction vessel equipped with a thermometer, a nitrogen gasintroducing tube and a stirrer, 664 parts of terephthalic acid, 631parts of isophthalic acid, 472 parts of 1,4-butanediol, 447 parts ofneopentyl glycol and 0.5 parts of dibutyltin oxide were charged whileintroducing a nitrogen gas and, after esterifying at 180 to 230° C. for5 hours, the polycondensation reaction was performed at 230° C. for 6hours until the acid value became 1 or less. After cooling to 120° C.,321 parts of adipic acid and 268 parts of 2,2′-dimethylolpropionic acidwere added and the mixture was heated to 170° C. again and then reactedat the same temperature for 20 hours to obtain a carboxylgroup-containing polyester polyol P-2 having an acid value of 46.5 and ahydroxyl value of 59.8 (see Table 1). TABLE 1 Formulation of rawmaterials of polyester polyol Polyester polyol P-2 Polyester AromaticPolyester polyol P-1 (containing polyol P-3 Aromatic carboxyl group)Aliphatic Terephthalic acid (Parts) 830 664 Isophthalic acid (Parts) 830631 Adipic acid (Parts) 321 1460 Ethylene glycol (Parts) 3741,4-butanediol (Parts) 472 1024 Neopentyl glycol (Parts) 598 4472,2′-dimethylolpropionic 268 acid (Parts) Molar ratio of dicarboxylicacid Aromatic/Aliphatic 10/0 8/2 0/10 Content of aromatic cyclic 34.8%25.2% 0.0% structural unit of polyester polyol Hydroxyl value (mgKOH/g)74.5 59.8 56.0 Acid value (mgKOH/g) 0.2 46.5 0.1 Number-averagemolecular 1500 1880 2000 weight<Preparation of Hydrophobic Polyester Polyol>

In a reaction vessel equipped with a thermometer, a nitrogen gasintroducing tube and a stirrer, 1660 parts of orthophthalic acid, 1637parts of diethylene glycol and 0.5 parts of dibutyltin oxide werecharged while charging a nitrogen gas and the polycondensation reactionwas performed at 230° C. for 15 hours until the acid value reaches 1 orless at 180 to 230° C. to obtain a polyester polyol Q-1 which has anaromatic cyclic structure and also has a hydroxyl value of 190 and anacid value of 0.3.

According to the formulation shown in Table 2, polyester polyols havingan aromatic cyclic structure Q-3 and Q-4 and a polyester polyol Q-2 wereobtained by the same procedure as described above.

<Preparation of Hydrophobic Polyether Polyol>

A liquid compound obtained by adding 2.8 mols of propylene oxide to 1mol of bisphenol A was referred to as a polyether polyol R. Theresulting polyether polyol R had a hydroxyl value of 282 and an aromaticcyclic structural unit content of 39.9%. TABLE 2 Formulation of rawmaterials of polyester polyol Polyester Polyester Polyester Polyesterpolyol Q-1 polyol Q-2 polyol Q-3 polyol Q-4 Aromatic Aliphatic AromaticAromatic Orthophthalic acid 1660 1660 (Parts) Adipic acid (Parts) 14601460 Diethylene glycol 1637 1637 (Parts) Ethylene glycol 1277 (Parts)bisphenol A 3523 (Parts) Hydroxyl value 190.0 205.0 440.0 119.0(mgKOH/g) Acid value 0.3 0.3 0.3 0.5 (mgKOH/g) Form of resin LiquidSolid Liquid Solid (25° C.) Content of 27.0% 0.0% 30.7% 51.8% aromaticcyclic structural unit

Example 1

1000 Parts of the polyester polyol P-1 was dehydrated at 100° C. underreduced pressure, cooled to 80° C. and then dissolved in 907 parts ofmethyl ethyl ketone while sufficiently stirring. After adding 80 partsof 2,2′-dimethylolpropionic acid and 281 parts of isophoronediisocyanate, the reaction was performed at 75° C. for 8 hours and theurethanization step was carried out.

After confirming that the isocyanate value became 0.1% or less andcooling to 50° C., 340 parts of the polyester polyol Q-1 was added toform a uniform solution. The solution was neutralized with 60 parts oftriethylamine and then water-dispersed by adding 7000 parts of water.

After removing methyl ethyl ketone from the resulting transparentreaction product at 40 to 60° C. under reduced pressure, theconcentration was adjusted by adding water to obtain a stabletransparent colloidal water dispersion having a nonvolatile content of20%.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were excellent in all physical properties, for example, adhesionto base material, conformability to base material, blocking resistance,solvent resistance, water resistance and ink adhesion (see Table 3-1).

Example 2

The same operation as in Example 1 was performed, except that 340 partsof the polyether polyol H was used in place of the polyester polyol Q-1of Example 1, as shown in Table 3-1, a stable transparent colloidalwater dispersion having a nonvolatile content of 20% was obtained.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were excellent in physical properties, as shown in Table 3-1.

Example 3

1000 Parts of the polyester polyol P-2 was dehydrated at 100° C. underreduced pressure, cooled to 80° C. and then dissolved in 812 parts ofmethyl ethyl ketone while sufficiently stirring. After adding 20 partsof 1,4-butanediol and 198 parts of dicyclohexylmethane-4,4′-diisocyanate(hydrogenated MDI), the reaction was performed at 75° C. for 8 hours.

After confirming that the isocyanate value became 0.1% or less andcooling to 50° C., 135 parts of the polyester polyol Q-1 was added andthe solution was neutralized with 84 parts of triethylamine and thenwater-dispersed by adding 7000 parts of water.

After removing methyl ethyl ketone from the resulting transparentreaction product at 40 to 60° C. under reduced pressure, theconcentration was adjusted by adding water to obtain a stabletransparent colloidal water dispersion having a nonvolatile content of20%.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were excellent in physical properties, as shown in Table 3-1.

Example 4

The same operation as in Example 1 was performed, except that 151 partsof the polyether polyol Q-3 was used in place of the polyester polyolQ-1 of Example 1, as shown in Table 3-1, a stable transparent colloidalwater dispersion having a nonvolatile content of 20% was obtained.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were excellent in physical properties, as shown in Table 3-1.

Example 5

The same operation as in Example 1 was performed, except that 583 partsof the polyether polyol Q-3 was used in place of the polyester polyolQ-1 of Example 1, as shown in Table 3-1, a stable transparent colloidalwater dispersion having a nonvolatile content of 20% was obtained.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were excellent in physical properties, as shown in Table 3-1.

Comparative Example 1

1000 Parts of the polyester polyol P-3 was dehydrated at 100° C. underreduced pressure, cooled to 80° C. and then dissolved in 897 parts ofmethyl ethyl ketone while sufficiently stirring. After adding 80 partsof 2,2′-dimethylolpropionic acid and 244 parts of isophoronediisocyanate, the reaction was performed at 75° C. for 8 hours.

After confirming that the isocyanate value became 0.1% or less andcooling to 50° C., 70 parts of the polyester polyol Q-1 was added andthe solution was neutralized with 53 parts of triethylamine and thenwater-dispersed by adding 7000 parts of water.

After removing methyl ethyl ketone from the resulting transparentreaction product at 40 to 60° C. under reduced pressure, theconcentration was adjusted by adding water to obtain a stabletransparent colloidal water dispersion having a nonvolatile content of20%.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were insufficient in adhesion to base material, blockingresistance and solvent resistance, as shown in Table 3-2.

Comparative Example 2

The same operation as in Example 1 was performed, except that thepolyester polyol Q-1 of Example 1 was not used, as shown in Table 3-2, astable transparent colloidal water dispersion having a nonvolatilecontent of 20% was obtained.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were inferior in film forming properties and were insufficient inOPP adhesion and conformability to base material, as shown in Table 3-2.

Comparative Example 3

The same operation as in Example 1 was performed, except that thepolyether polyol Q-2 was used in place of the polyester polyol Q-1 ofExample 1, as shown in Table 3-2. As a result, a stable water dispersioncould not be obtained because of poor compatibility between thepolyurethane resin and the polyether polyol Q-2.

Comparative Example 4

The same operation as in Example 1 was performed, except that thepolyether polyol Q-4 was used in place of the polyester polyol Q-1 ofExample 1, as shown in Table 3-2, a stable transparent colloidal waterdispersion having a nonvolatile content of 20% was obtained.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were inferior in film forming properties and were insufficient inadhesion to OPP base material and conformability to base material, asshown in Table 3-2.

Comparative Example 5

800 Parts of the polyester polyol P-1 and 200 parts of the polyesterpolyol Q-1 were dehydrated at 100° C. under reduced pressure, cooled to80° C. and then dissolved in 977 parts of methyl ethyl ketone whilesufficiently stirring. After adding 80 parts of 2,2′-dimethylolpropionicacid and 385 parts of dicyclohexylmethane-4,4′-diisocyanate(hydrogenated MDI), the reaction was performed at 75° C. for 8 hours.

After confirming that the isocyanate value became 0.1% or less andcooling to 50° C., the solution was neutralized with 60 parts oftriethylamine and then water-dispersed by adding 7000 parts of water.After removing methyl ethyl ketone from the resulting transparentreaction product at 40 to 60° C. under reduced pressure, theconcentration was adjusted by adding water to obtain a stabletransparent colloidal water dispersion having a nonvolatile content of20%.

Using the resulting water dispersion, aqueous coating agents A and Bwere prepared in the same manner as described above and variousevaluations were performed. As a result, the resulting aqueous coatingagents were insufficient in film forming properties and conformabilityto base material, as shown in Table 3-2, because the plasticizationeffect due to the hydrophobic polyol (B) is not exerted. TABLE 3-1Evaluation results of Examples Example 1 Example 2 Example 3 Example 4Example 5 Water-dispersible polyurethane resin (A) Polyester polyol P-1(Parts) 1000 1000 1000 1000 Polyester polyol P-2 (Parts) 10002,2′-dimethylolpropionic acid (Parts) 80 80 80 80 1,4-butanediol (Parts)20 Hydrogenated MDI 1) (Parts) 198 Isophorone diisocyanate (Parts) 281281 281 281 Polyisocyanate compound content 20.6% 20.6% 16.3% 20.6%20.6% Content of aromatic cyclic structural unit of 25.6% 25.6% 20.7%25.6% 25.6% water-dispersible polyurethane resin (A) Hydrophobic polyol(B) Polyester polyol Q-1 (Parts) 340 135 Polyester polyol Q-3 (Parts)151 583 Polyether polyol R (Parts) 340 Polyurethane resin (A)/Polyol (B)80/20 80/20 90/10 90/10 70/30 (weight ratio) Film forming properties 5°C. A A A to B A A 20° C. A A A A A Adhesive tape peeling test PETadhesion Aqueous coating agent A 5 5 5 5 5 Aqueous coating agent B 5 5 55 5 OPP adhesion Aqueous coating agent A 5 5 5 5 5 Aqueous coating agentB 5 5 5 5 5 Conformability to base material A A A A A Blockingresistance A A A A A Solvent resistance 5 4 5 5 4 Water resistance 5 4 55 4 Ink adhesion 5 5 5 5 5Note 1)hydrogenated MDI: dicyclohexylmethane-4,4′-diisocyanate

TABLE 3-2 Evaluation results of Comparative Examples ComparativeComparative Comparative Comparative Comparative Example 1 Example 2Example 3 Example 4 Example 5 Water-dispersible polyurethane resinPolyester polyol P-1 (Parts) 1000 1000 1000 800 Polyester polyol P-2(Parts) Polyester polyol P-3 (Parts) 1000 Polyester polyol Q-1 (Parts)200 2,2′-dimethylolpropionic acid (Parts) 80 80 80 80 80 1,4-butanediol(Parts) Hydrogenated MDI 1) (Parts) 385 Isophorone diisocyanate (Parts)244 281 281 281 Polyisocyanate compound content 18.4% 20.6% 20.6% 20.6%26.3% Content of aromatic cyclic structural unit 0.0% 25.6% 25.6% 25.6%22.7% of water-dispersible polyurethane resin HydrophobicpolyolPolyester polyol Q-1 (Parts) 70 Polyester polyol Q-2 (Parts) 340Polyester polyol Q-4 (Parts) 340 Polyurethane resin (A)/polyol (B)(weight ratio) 95/5 100/0 80/20 80/20 copolymerized Film formingproperties 5° C. A C 2) C C 20° C. A C C C Adhesive tape peeling testPET adhesion Aqueous coating agent A 1 5 5 5 Aqueous coating agent B 2 55 5 OPP adhesion Aqueous coating agent A 3 1 1 2 Aqueous coating agent B3 1 2 2 Conformability to base material A C C C Blocking resistance B AA A Solvent resistance 1 5 5 5 Water resistance 2 5 5 5 Ink adhesion 1 55 5Note 2):imppossible to perform water dispersion

INDUSTRIAL APPLICABILITY

The aqueous coating agent of the present invention has excellentprocessability in a wide temperature range and excellent adhesion toplastic films because of its excellent film forming properties at lowtemperature, and is also excellent in blocking resistance, waterresistance, solvent resistance and transparency and, therefore, theaqueous coating agent is suited for use as a coating agent for plasticfilms, which are used in in-line coating and off-line coating methods.The aqueous coating agent can be widely used as a primer coating agentor anchor coating agent in the fields of food packaging films,decorative materials and metal deposited films, and also used as acoating composition, ink, and surface treating agent for fibers andleathers.

1. An aqueous coating agent comprising: a water dispersion (C) preparedby dispersing resin particles containing a water-dispersiblepolyurethane resin (A) and at least one compound selected from ahydrophobic polyester polyol (B-1) and a hydrophobic polyether polyol(B-2) in water, and a crosslinking agent (D) capable of reacting with ahydroxyl group, wherein the water-dispersible polyurethane resin (A) isobtained by reacting a polyester polyol (a-1), which is obtained bycondensing a dicarboxylic acid containing an aromatic dicarboxylic acidas a main component with a polyol, with a polyisocyanate, and alsocontains 15 to 35% by weight of an aromatic cyclic structural unit basedon the weight of the water-dispersible polyurethan resin (A), andwherein the hydrophobic polyester polyol (B-1) and/or the hydrophobicpolyether polyol (B-2) are liquid at normal temperature and contain 20to 50% by weight of an aromatic cyclic structural unit.
 2. The aqueouscoating agent according to claim 1, wherein the total content of aurethane-bond unit and a urea-bond unit per 1000 g of thewater-dispersible polyurethane resin (A) is within a range from 1.0 to4.0 mols.
 3. The aqueous coating agent according to claim 1, wherein thehydrophobic polyester polyol (B-1) is obtained by condensing adicarboxylic acid with an aliphatic diol having 2 to 8 carbon atoms, andorthophthalic acid accounts for at least 60 mol % of the total amount ofthe dicarboxylic acid.
 4. The aqueous coating agent according to claim1, wherein the hydrophobic polyether polyol (B-2) is a propylene oxideadduct of a polynuclear phenol compound.
 5. The aqueous coating agentaccording to claim 1, wherein the water-dispersible polyurethane resin(A) is obtained by reacting a polyester polyol (a-1), which is obtainedby condensing a dicarboxylic acid with a polyol, with a polyisocyanate,and at least one compound selected from terephthalic acid andisophthalic acid accounts for 70 to 100 mol % of the total amount of thedicarboxylic acid.
 6. The aqueous coating agent according to claim 1,wherein the water-dispersible polyurethane resin (A) and the hydrophobicpolyester polyol (B-1) or the hydrophobic polyether polyol (B-2) are notsubstantially chemically-bonded.
 7. The aqueous coating agent accordingto claim 1, wherein the crosslinking agent (D) is at least one kindselected from the group consisting of an amino resin and apolyisocyanate.